Filling the historiographical gap created by an overemphasis upon its rival Liberal and Labour parties, this study analyses the part played by the war in shaping Unionist (later Conservative) fortunes between 1914-18. The first two chapters consider the internal party dynamic between leaders, MPs and grassroots supporters, and scrutinise the effect of war upon the central tenets of the Unionist Party (most especially Ireland). The third and fourth chapters concentrate. respectively upon the party's reaction to the threat of socialism and Bolshevism, and the response to the onset of a mass electorate and of class politics in 1918. The fifth chapter investigates the party's approach to state intervention during the war and its immediate aftermath. The thesis shows that a primary Unionist response to the rise of the Labour Party was the construction of an appeal based on the wartime link between patriotism and anti-socialism. Bolstered by state propaganda and the press, this served to clarify the party's approach through into the 1920s and to counter the Labour Party at a crucial juncture in its evolution. It shows how patriotism preserved the unity of Unionism and shaped its ideological development. Patriotism also dictated the primacy accorded to economic, social and national efficiency, and thus shaped responses generated towards post-war reconstruction, most notably in the emphasis upon competition along international rather than internal lines. Moreover, because the `total' war was viewed as placing exceptional but temporary demands upon the economy and society, the party was able to adapt itself to war and post-war challenges in a flexible manner distinct from that of its counterparts. This however determined that the coalition with Lloyd George and notions of reconstruction were also viewed principally as short-term necessities to ensure military victory and social stability in the immediate years of recovery. Taken together, these conclusions illustrate the Conservative Party's organic ideological development into a group committed to the protection of property, and its willingness to utilise the means of the state and propaganda to make its anti-socialist message a viable goal.